At present, required peak rates of up to 1 Gbps in the downlink and 500 Mbps in the uplink in a Long Term Evolution-Advanced (LTE-A) system have been significantly improved as compared to a Long Term Evolution (LTE) system while requiring good compatibility of the LTE-A system with the LTE system. Thus Carrier Aggregation (CA) has been introduced to the LTE-A system so as to accommodate the required improved peak rates, compatibility with the LTE system and full use of spectrum resources.
The CA technology refers to that a user equipment is configured by the network side with a plurality of cells so that the user equipment can operate on the plurality of cells simultaneously, where a cell includes a pair of uplink and downlink (UL and DL) Component Carriers (CCs) or only a DL CC. To the contrary, a user equipment is configured with only one cell in the LTE system and earlier wireless communication systems. In the CA-enabled LTE-A system, respective CCs can be spectrally consecutive or inconsecutive, and the respective CCs can have the same or different bandwidths, and in order to maintain compatibility with the LTE system, there is a limited maximum bandwidth of 20 MHz per CC. At present a user equipment is generally configured with five cells at most.
Moreover carrier-aggregated cells are further categorized as follows in LTE-A:
A Primary Cell (PCell) refers to the only one cell defined as a PCell among a plurality of aggregated cells configured for a UE.
A Secondary Cell (SCell) refers to all the other cells than the PCell among the plurality of aggregated cells configured for the UE.
The PCell is selected at the network side and configured for the user equipment by RRC signaling, and different user equipments can have different PCells. As specified in the LTE R10 version, the difference between the PCell and the SCell lies in that the PCell is bound with a variety of functions, where the following general functions are bound with the PCell:
A Physical Uplink Control Channel (PUCCH) is configured only for the PCell to transmit a Channel State Indicator (CSI), Hybrid Automatic Repeat reQuest (HARM) Acknowledgement/Non-acknowledgement (ACK/NACK) feedback information and a Dedicated Scheduling Request (DSR);
The downlink of the PCell can act as a UL timing reference for a random access;
The PCell can act as a pathloss reference for the PCell and the other SCells;
A random access can be performed only in the PCell;
A Semi-Persistent Scheduling (SPS) resource can be configured only in the PCell; and
A Radio Link Failure (RLF) of the user equipment can be judged only if there is an RLF occurring in the PCell.
As specified in the R8/9 versions, the following seven UL/DL configurations as depicted in Table 1 are defined for a Time Division Duplex (TDD) system in the physical layer standard, where D represents a DL subframe, U represents a UL subframe, S represents a special subframe of the TDD system, and configuration # “0-6” correspond respectively to the seven UL/DL configurations. For example, the configuration # “2” represents ten subframes included in a frame, which are configured respectively as “D, S, U, D, D, D, S, U, D, D”.
TABLE 1UL/DLSubframe number#Configuration#01234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
Along with technological development, as specified in the R11 version, a user equipment configured with aggregated cells in the LTE-A system can share or use an adjacent band with another system (e.g., the LTE system), and referring to FIG. 1, for example, a user equipment is configured with three aggregated cells including a cell 1, a cell 2 and a cell 3 in the LTE-A system, where the cell 1 and the cell 2 use the same band, i.e., Band 1, and the cell 3 uses a band, i.e., Band 2. In order to avoid uplink and downlink cross interference in the TDD system, the Band 1 and the adjacent TDD band A in a 3G/LTE (3G system or LTE system) have to use TDD UL/DL configurations that can coexist with each other, where the so-called TDD UL/DL configurations that can coexist with each other refer to TDD UL/DL configurations without UL/DL cross interference, that is, the same TDD UL/DL configuration for the LTE system; and the Band 2 and the corresponding 3G/LTE TDD Band B have to use TDD UL/DL configurations that can coexist with each other. If the Band A and the Band B use different TDD UL/DL configurations, then the Band 1 and the Band 2 also use different TDD UL/DL configurations.
However the existing LTE-A system has been designed based on the R10 version, and as specified in the R10 version, only intra-band CA (i.e., carrier aggregation within the same band) is supported in the UL in a CA scenario, so the pathloss reference for transmission over a UL CC can be defined as the DL CC corresponding to the UL CC, which is broadcasted in a broadcast message, or the DL CC of a PCell. The DL CC of the PCell can be defined as the pathloss reference because the UL CC of a user equipment and the UL CC of the PCell of the user equipment are in the same band as specified in the R10 version, thus the pathloss is similar.
Also as defined in the R10 version, a Discontinuous Reception (DRX) mechanism refers to that aggregated cells for a user equipment have the same Active Time. The so-called Active Time refers to a period of time for which the user equipment has to listen to the control channel. Referring to FIG. 2, an On Duration represents a period of time for which a UE listens to the control channel, when the radio frequency channel is opened and the control channel is listened to continuously, and the On Duration typically periodically occurs (i.e., a DRX cycle), and a specific cycle is configured by an eNB.
As can be apparent from the foregoing description, a carrier aggregation-enabled user equipment in R11 supports different TDD UL/DL configurations, and if R10 specification is directly applied to R11, it may result in the following numerous problems.
1. If a user equipment is configured with a plurality of aggregated cells based on the CA technology and each cell uses a different TDD UL/DL configuration, and if there is a large interval between bands corresponding to the respective cells, as illustrated in FIG. 1, for example, the cell 1 and the cell 2 correspond to the Band 1, and the cell 3 corresponds to the Band 2, then the pathloss condition of the PCell can not be regarded as the pathloss reference of any other SCell regardless of which cell of the cell 1, the cell 2 and the cell 3 is the PCell.
2. As specified in the R10 version, a user equipment only reads broadcast information on the PCell and the system information of the other SCells is notified by dedicated signaling, but existing dedicated signaling to indicate system information of an SCell does not indicate the TDD UL/DL configuration of this SCell and its TDD UL/DL configuration is regarded same as the PCell by default, so the existing R10 mechanism can not support the use of different TDD UL/DL configurations respectively for a plurality of different cells aggregated for a user equipment.
3. If a user equipment is configured with a plurality of aggregated cells based on the CA technology and each cell uses a different TDD UL/DL configuration, then there may be a resource waste if there is an cross-carrier scheduling relationship between the cells with different TDD UL/DL configurations.
Referring to FIG. 1 and FIG. 3, for example, if there are different TDD UL/DL configurations in cell 1 and cell 2, and cell 1 can cross-carrier schedule cell 2 which is indicated by a higher layer, then cell 2 will be a cell with only Physical Downlink Shared Channel (PDSCH), that is, no PDCCH to schedule the user equipment is borne in cell 2, and thus as illustrated in FIG. 3 and as specified in the R10 version, for cross-carrier scheduling, the cell 1 can schedule the downlink of subframe 0 and the uplink of subframe 4 of cell 1 and the downlink of subframe 0 and the uplink of subframe 4 of the cross-carrier scheduled cell 2 in subframe 0, But the TDD UL/DL configuration of subframe 4 in cell 2 is downlink, thus the subframe 4 of cell 2 cannot be scheduled by subframe 0 of cell 1 because downlink subframe can only be scheduled by itself, which will result the resource waste of cell 2 in certain subframes.
4. As specified in the R10 version, when a plurality of cell configured for a user equipment based on the CA technology transmit data in the same subframe, their corresponding Hybrid Automatic Repeat Request (HARQ) ACK/NACK information is fed back at the same instance of time. As specified in the R11 version, different cells configured for a user equipment can use different TDD UL/DL configurations, so when the different cells configured for the user equipment transmit data in the same subframe, their corresponding HARQ ACK NACK information is fed back at different instances of time, thus complicating a PUCCH design.
Referring to FIG. 1 and FIG. 4, for example, the Band 1 uses a TDD UL/DL configuration with the configuration #0, and the Band 2 use a TDD UL/DL configuration with the configuration #2, and if both the Band 1 and the Band 2 have a DL PDSCH transmitted at the same instance of time (in the subframe 0), then ACK information corresponding to PDSCH transmission in the Band 1 and the Band 2 is fed back at different instances of time, thus complicating a PUCCH design.
As can be apparent the use of different TDD UL/DL configurations for a plurality of different cells aggregated for a user equipment actually can not be supported in the prior art, and it is thus desirable in the R11 version to introduce a new mechanism so as to ensure normal operation of the system even in this situation.